A basic rule for getting control surfaces that will give good response and allow reasonable aerobatics would be to have the area ailerons be about 10%-15% of the total wing area, and the elevators to be 10%-15% of the total horizontal tail area. Rudder can be 15%-20% of the total vertical tail area. Of course, you can make them larger if you want the airplane to be able to perform more extreme aerobatics. Some of the 3-D type airplanes have ailerons in excess of 25% of the total wing area, and elevators in excess of 50% of the total horizontal tail area. Some of those types have a rudder that's 60%-75% of the total vertical tail area.

With any design, you must make compromises. If you have very large control surfaces, moderate maneuvering will require very little control throw, but will also be much more prone to flutter. Smaller surfaces will have less tendency to flutter, but will require more deflection. Also, you must design a little bit as to what "looks good".

One easy way to determine the size is to look at other models that have a similar performance envelope to what you want to do, and use areas and moments that are similar. You'll wind up with a plane that will fly quite well.